The allantois or allantoic sac is a portion of an avian egg that develops and then enlarges in the egg from about the 5.sup.th to 13.sup.th day, and thereafter is absorbed and diminishes in size until the egg is hatched. The allantoic sac functions as a respiratory surface, a calcium adsorbing tissue, a liquid waste receptacle for urine secreted by the mesonephros, and as a water reservoir to sustain later stage development of the embryo. The allantoic sac reaches its peak volume at about the 11.sup.th day of incubation and begins to diminish in size after about the 13.sup.th day. Because the allantoic sac essentially grows to surround the embryo, it normally exists as a relatively thin layer under the inner shell membrane which presents a difficult target for injection even during the period of maximum volume.
Methods for producing influenza and other viral vaccines involve the growth of the viruses in embryonated chicken eggs. Typically, each egg must be inoculated by injection of a small volume of virus into the allantoic cavity. The injected eggs are then incubated and opened to allow harvesting of the allantoic fluid and the virus growing therein. See, e.g., U.S. Pat. No. 4,338,296 to Lobmann.
Additionally, various materials may be injected into the avian embryo in ovo, or into the various compartments within the embryonated avian egg, to achieve beneficial effects in a subsequently hatched chick. Such beneficial effects include increased growth, prevention of disease, increasing the percentage hatch of multiple incubated eggs, and otherwise improving physical characteristics of hatched poultry. Additionally, certain types of vaccinations are suitable for in ovo administration (see U.S. Pat. No. 4,458,630 to Sharma).
One method of sampling or injecting the allantoic fluid of an avian egg involves candling of individual eggs to locate the allantois, and then injecting or sampling the allantois by hand using a syringe. Injection into the allantois by hand has been practiced in the biological sciences for the purpose of culturing various microorganisms therein. However, because of the difficulty of reliable targeting the allantois using high volume or automated methods, the poultry industry has not generally used the allantois as a target for injection.
A number of automatic egg injection devices have been developed. These include U.S. Pat. Nos. 5,056,464 to Lewis; U.S. Pat. Nos. 4,903,635 and 4,681,063 to Hebrank; U.S. Pat. No. 5,136,979 to Paul et al.; and U.S. Pat. Nos. 4,040,388, 4,469,047 and 4,593,646 to Miller, which are incorporated herein by reference in their entirety.
Recently, efforts by the poultry industry to inject into the allantois using vertical downward injection through the large end of a vertically oriented egg by traversing the air sac and air sac membrane have been reported, but efforts to accomplish this on a large scale using conventional egg injection equipment have produced mixed results with a significant number of injections discharging into the air sac or the amnion instead of the allantois. It is therefore an object of the present invention to provide a method whereby the allantoic sac may be reliably targeted for injection with, for example, microorganisms that are to be cultivated in the egg or materials that are beneficial to the embryo. It is a further object of the present invention to provide a method whereby the allantoic sac may be reliably targeted for piercing with a probe such as a hypodermic needle for purposes of analyzing or sampling the allantoic fluid contained therein. It is a further object of the present invention to provide an improved method for reliably injecting into the allantois of an egg on a large scale using conventional egg injection equipment, and to provide a method that injects or reaches the allantois without piercing the air cell membrane. It is a further object of this invention to provide a method for utilizing an improved egg tray in the process of injecting into the allantois of an egg on a large scale using conventional egg equipment. These and other objects of the invention will be apparent to those skilled in the art in view of the ensuing description and claims.